System and technique for creating implanted regions using multiple tilt angles

ABSTRACT

A system and method for creating various dopant concentration profiles using a single implant energy is disclosed. A plurality of implants are performed at the same implant energy but different tilt angles to implant ions at a variety of depths. The result of these implants may be a rectangular profile or a gradient profile. The resulting dopant concentration profile depends on the selection of tilt angles, doses and the number of implants. Varying tilt angle rather than varying implant energy to achieve implants of different depths may significantly improve efficiency and throughput, as the tilt angle can be changed faster than the implant energy can be changed. Additionally, this method may be performed by a number of different semiconductor processing apparatus.

FIELD

Embodiments of this disclosure are directed to systems and methods forforming implanted regions having a dopant concentration profile thatcannot be created using a single implant, and more particularly forcreating implanted regions having a rectangular or gradient profileusing a single implant energy and multiple tilt angles.

BACKGROUND

There are various semiconductor devices which utilize an implantedregion having a predefined dopant concentration profile embedded in theworkpiece.

One specific type of device is referred to as an insulated gate bipolartransistor (IGBT). An IGBT combines concepts from bipolar transistorsand MOSFETs to achieve an improved power device. The emitter and thegate are disposed on one side of the device, while the collector isdisposed on the opposite second side of the device. The emitter is incommunication with a heavily p-doped region disposed directly below theemitter. On either side of the heavily p-doped region are heavilyn-doped regions, each in communication with the gate. Beneath theheavily p-doped region is a lightly p-doped region. On the opposite sideof the device is a second heavily p-doped region, in communication withthe collector. Finally, between the second heavily p-doped region andthe lightly p-doped region is a lightly n-doped drift layer.

In conventional IGBT devices, the thickness of the lightly n-doped driftlayer is determined based on the need to sustain the electrical field.As the power ratings for these devices increases, the overall thicknessof the device also increases.

One technique to reduce the thickness of these IGBT transistors is toincorporate a heavily n-doped field stop layer between the lightlyn-doped drift layer and the second heavily p-doped region. Theelectrical field decreases rapidly within this field stop layer,allowing thinner devices to be created. In certain embodiments, thefield stop layer has a rectangular or box profile.

In certain embodiments, this field stop layer is created by implantingions, such as hydrogen ions, into the lightly n-doped drift layer. Thisfield stop layer may be disposed adjacent to the second heavily p-dopedregion.

Additionally, the field stop layer may have a thickness that is 1 ormore μm. Creating an implanted region of this thickness typicallyinvolves a plurality of implants, each done at a different implantenergy.

Other types of devices also make use of specially implanted regions. Forexample, photodiodes typically have a deep trench for isolation andlogic devices typically implement P-wells and N-wells. In each of thesedevices, the implanted region is traditionally formed using a pluralityof implants, each at a different implant energy.

In certain embodiments, the desired dopant concentration profile of theimplanted region may resemble a box or rectangle, where theconcentration remains roughly constant over a range of depths. In otherembodiments, the desired dopant concentration profile of the implantedregion may be a gradient profile, where the desired concentrationprofile varies with depth.

However, changing the implant energy of a semiconductor implantationsystem is time consuming. Specifically, the voltages applied to variouselectrodes, accelerators, acceleration/deceleration stages, magnets, andfocusing elements is changed for each of these implant energies.Modifying these voltages may take many minutes. Thus, throughput andutilization are greatly affected by the modification of the implantenergy.

Therefore, it would be beneficial if there was a method of processing asemiconductor workpiece that could create implanted regions having thesedesired dopant concentration profiles in a more efficient manner.Further, it would be advantageous if this method was applicable to avariety of different types of semiconductor processing equipment.

SUMMARY

A system and method for creating various dopant concentration profilesusing a single implant energy is disclosed. A plurality of implants areperformed at the same implant energy but different tilt angles toimplant ions at a variety of depths. The result of these implants may bea rectangular profile or a gradient profile. The resulting dopantconcentration profile depends on the selection of tilt angles, doses andthe number of implants. Varying tilt angle rather than varying implantenergy to achieve implants of different depths may significantly improveefficiency and throughput, as the tilt angle can be changed faster thanthe implant energy can be changed. Additionally, this method may beperformed by a number of different semiconductor processing apparatus.

According to one embodiment, a method of forming an implanted regionhaving a rectangular concentration profile within a semiconductorworkpiece is disclosed. The method comprises performing a first implanton the semiconductor workpiece, wherein the first implant is performedat a predetermined implant energy and a first tilt angle, wherein amaximum concentration of ions implanted by the first implant occurs at afirst depth; and performing a second implant on the semiconductorworkpiece, wherein the second implant is performed at the predeterminedimplant energy and a second tilt angle, wherein the maximumconcentration of ions implanted by the second implant occurs at a seconddepth, less than the first depth; wherein the second tilt angle isselected such that, after the first and second implants are performed, aminimum concentration between the first depth and the second depth isgreater than a predetermined minimum concentration. In certainembodiments, the first tilt angle is at or near 0° and the predeterminedimplant energy is selected such the first depth is at a desired depth.In some embodiments, the method comprises performing a third implant onthe semiconductor workpiece, wherein the third implant is performed atthe predetermined implant energy and a third tilt angle, greater thanthe second tilt angle, wherein the maximum concentration of ionsimplanted by the third implant occurs at a third depth, less than thefirst depth and the second depth; wherein the third tilt angle isselected such that, after the first, second and third implants areperformed, a minimum concentration between the first depth and the thirddepth is greater than the predetermined minimum concentration. In someembodiments, a thickness of the implanted region, wherein thickness isdefined as a maximum depth having a concentration greater than thepredetermined minimum concentration, less a minimum depth having theconcentration greater than the predetermined minimum concentration, isgreater than 1 μm. In certain embodiments, the thickness of theimplanted region is greater than 2 μm. In some embodiments, a ratio of amaximum concentration between the first depth and the third depth to theminimum concentration is less than 5. In certain embodiments, the ratioof the maximum concentration to the minimum concentration is less than4. In certain embodiments, the ratio of the maximum concentration to theminimum concentration is less than 3. In some embodiments, the firstimplant is performed with a first dose, the second implant is performedwith a second dose and the third implant is performed with a third dose,wherein the first dose, the second dose and the third dose are not allthe same value. In some embodiments, one or more additional implants areperformed at additional tilt angles, between the first tilt angle andthe third tilt angle, so as to reduce a ratio of a maximum concentrationbetween the first depth and the third depth to the minimumconcentration.

According to another embodiment, a semiconductor processing apparatus isdisclosed. The apparatus comprises an ion source to generate ions; anaccelerator to provide energy to the ions; a platen to hold asemiconductor workpiece; a platen orientation motor to adjust a tiltangle of the platen; and a controller; wherein the controller isconfigured to create an implanted region having rectangularconcentration profile in the semiconductor workpiece, wherein thecontroller: sets an implant energy by adjusting a voltage supplied tothe accelerator; sets a first tilt angle using the platen orientationmotor; performs a first implant at the implant energy and the first tiltangle, wherein a maximum concentration of ions implanted in thesemiconductor workpiece by the first implant occurs at a first depth;sets a second tilt angle using the platen orientation motor; performs asecond implant at the implant energy and the second tilt angle, whereinthe maximum concentration of ions implanted in the semiconductorworkpiece by the second implant occurs at a second depth, less than thefirst depth; sets a third tilt angle using the platen orientation motor;and performs a third implant at the implant energy and the third tiltangle, wherein the maximum concentration of ions implanted in thesemiconductor workpiece by the third implant occurs at a third depth,less than the first depth and the second depth; wherein the first tiltangle, the second tilt angle and the third tilt angle are selected suchthat a minimum concentration between the first depth and the third depthis greater than a predetermined minimum concentration, and a ratio of amaximum concentration to the minimum concentration is less than 5. Insome embodiments, the first implant is performed with a first dose, thesecond implant is performed with a second dose and the third implant isperformed with a third dose, wherein the first dose, the second dose andthe third dose are not all the same value. In certain embodiments, thecontroller performs one or more additional implants at additional tiltangles, between the first tilt angle and the third tilt angle, so as toreduce the ratio of a maximum concentration to the minimumconcentration. In certain embodiments, the first tilt angle, the secondtilt angle and the third tilt angle are selected such that the ratio ofthe maximum concentration to the minimum concentration is less than 3.

According to another embodiment, a method of forming an implanted regionhaving a gradient concentration profile within a semiconductor workpieceis disclosed. The method comprises performing a first implant on thesemiconductor workpiece, wherein the first implant is performed at apredetermined implant energy, a first dose and a first tilt angle; andperforming a second implant on the semiconductor workpiece, wherein thesecond implant is performed at the predetermined implant energy, asecond dose and a second tilt angle; wherein the first tilt angle, thefirst dose, the second tilt angle, and the second dose are selected suchthat, after the first and second implants are performed, a concentrationof implanted atoms decreases between a first depth and a second depth.In certain embodiments, when plotted on a semi-log graph, a profile ofthe concentration of implanted atoms decreases roughly linearly betweenthe first depth and the second depth. In some embodiments, the firstdose is different from the second dose. In some embodiments, the methodfurther comprises performing a third implant on the semiconductorworkpiece, wherein the third implant is performed at the predeterminedimplant energy, a third dose and a third tilt angle; wherein the thirdtilt angle and the third dose are selected such that, after the first,second and third implants are performed, when plotted on a semi-loggraph, a profile of the concentration of implanted atoms decreasesroughly linearly between the first depth and the second depth. Incertain embodiments, one of the implants is performed at a tilt angle toallow channeling of atoms in the semiconductor workpiece.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, which are incorporated herein by referenceand in which:

FIG. 1A shows a semiconductor processing apparatus that may be utilizedaccording to one embodiment;

FIG. 1B shows a semiconductor processing apparatus that may be utilizedaccording to a second embodiment;

FIG. 1C shows a semiconductor processing apparatus that may be utilizedaccording to a third embodiment;

FIG. 2 shows four implants performed at the same implant energy butdifferent tilt angles;

FIG. 3 shows the concentration of ions in the workpiece after the fourimplants shown in FIG. 2; and

FIG. 4 shows a gradient concentration profile created by three implantsperformed at the same implant energy but different tilt angles; and

FIG. 5 shows the three implants used to generate the dopantconcentration profile shown in FIG. 4.

DETAILED DESCRIPTION

The present disclosure describes the use of multiple tilt angles toenable the formation of implanted regions having a desired dopantconcentration profile in a workpiece without modifying the implantenergy. This technique is applicable to various types of semiconductorprocess apparatus. Several of these apparatuses are described below.

As shown in FIG. 1A, a semiconductor processing apparatus comprises anion source 100, which is used to generate an ion beam. In oneembodiment, a positive ion beam 101 may be created in the traditionalmanner, such as using a Bernas or indirectly heated cathode (IHC) ionsource. Of course, other types of ion sources may also be employed. Afeedgas is supplied to the ion source 100, which is then energized togenerate ions. In certain embodiments, the feedgas may be hydrogen,boron, phosphorus, arsenic, helium, or other suitable species.Extraction optics are then used to extract these ions from the ionsource 100.

The positive ion beam 101 exiting the ion source 100 may be coupled to aMg charge exchange cell 110, which transforms the positive ion beam 101into a negative ion beam 111. Of course, other mechanisms for thegeneration of a negative ion beam are known in the art. The mechanismused to create the negative ion beam is not limited by this disclosure.

The negative ion beam 111 may be directed toward a mass analyzer 120,which only allows the passage of certain species of ions. The negativeions that exit the mass analyzer 120 are directed toward a tandemaccelerator 130.

The tandem accelerator 130 has two pathways, which are separated by astripper tube 133. The input pathway 131 comprises a plurality of inputelectrodes. These input electrodes may be any suitable electricallyconductive material, such as titanium or other metals. The outermostinput electrode may be grounded. Each of the subsequent input electrodesmay be biased at an increasingly more positive voltage moving closer tothe stripper tube 133.

The input pathway 131 leads to the stripper tube 133. The stripper tube133 is biased positively relative to the outermost input electrode. Thestripper tube 133 includes an injection conduit where a stripper gas isinjected. The stripper gas may comprise neutral molecules. These neutralmolecules may be any suitable species such as, but not limited to argonand nitrogen. The stripper tube 133 has an inlet disposed on the sameside as the input pathway 131. The outlet of the stripper tube 133 is incommunication with the output pathway 132.

In other words, the stripper tube 133 is positively biased so as toattract the negative ion beam 111 through the input pathway 131. Thestripper tube 133 removes electrons from the incoming ions, transformingthem from negative ions into positive ions.

The stripper tube 133 is more positive than the electrodes in the outputpathway 132. Each subsequent output electrode may be less positivelybiased moving away from the stripper tube 133. For example, theoutermost output electrode may be grounded. Thus, the positive ions inthe stripper tube 133 are accelerated through the output pathway 132.

In this way, the ions are accelerated two times. First, negative ionsare accelerated through the input pathway 131 to the stripper tube 133.This acceleration is based on the difference between the voltage of theoutermost input electrode and the voltage of the stripper tube 133.Next, positive ions are accelerated through the output pathway 132. Thisacceleration is based on the difference between the voltage of thestripper tube 133 and the voltage of the outermost output electrode inthe output pathway 132.

An accelerator power supply 134 may be used to supply the voltages tothe stripper tube 133, as well as the electrodes in the input pathway131 and the output pathway 132. The accelerator power supply 134 may becapable of supply a voltage up to 2.5 MV, although other voltages,either higher or lower, are also possible. Thus, to modify the implantenergy, the voltage applied by the accelerator power supply 134 ischanged.

After exiting the tandem accelerator 130, the positive ion beam 135 mayenter a filter magnet 140, which allows passage of ions of only acertain charge. In other embodiments, the filter magnet 140 may not beemployed. The output of the filter magnet 140 may pass through a scanner150, which serve to create the final ion beam 155 containing the desiredspecies of ions. The scanner 150 causes the incoming ion beam to befanned in the width direction so as to form a scanned ribbon ion beam.The output of the scanner 150 is then directed toward a platen 160. Aworkpiece 10 may be disposed on the platen 160. In certain embodiments,a corrector magnet may be disposed between the scanner 150 and theplaten 160.

The platen 160 may be in communication with a platen orientation motor170. The platen orientation motor 170 may be configured to move theplaten 160 in any of a plurality of different directions. For example,the platen orientation motor 170 may have the capability to rotate theplaten 160. Rotation occurs about an axis that is normal to the surfaceof the platen 160 and passes through the center of the workpiece (orplaten). The angle of rotation may be referred to as the twist angle.

Additionally, the platen orientation motor 170 is configured to tilt theplaten 160. Tilt is defined as a rotation about an axis 161 that isparallel to the wider dimension of the ion beam and passing through thecenter of the platen 160. This tilt is sometimes referred to as X-tilt.The angle of X-tilt may be referred to as the tilt angle.

Additionally, the semiconductor processing apparatus includes acontroller 180. The controller 180 may include a processing unit, suchas a microcontroller, a personal computer, a special purpose controller,or another suitable processing unit. The controller 180 may also includea non-transitory computer readable storage element, such as asemiconductor memory, a magnetic memory, or another suitable memory.This non-transitory storage element may contain instructions and otherdata that allows the controller 180 to perform the functions describedherein.

The controller 180 may be in communication with the accelerator powersupply 134, so as to control the implant energy. In addition, thecontroller 180 may be in communication with the platen orientation motor170, so as to adjust the tilt angle and twist angle of the platen 160.The controller 180 may also be in communication with other components.

A second embodiment is shown in FIG. 1B. Components that are common withFIG. 1A are given identical reference designators.

As described above, a semiconductor processing apparatus comprises anion source 100, which is used to generate an ion beam. The ion source100 has an aperture through which ions may be extracted from the ionsource 100. These ions may be extracted from the ion source 100 byapplying a negative voltage to the extraction optics 103 disposedoutside the ion source 100, proximate the extraction aperture. Theextraction optics 103 may be pulsed so that ions exit at specific times.The group of ions that exits may be referred to as a bunch. In oneembodiment, a plurality of bunched ions may be created. The ions maythen enter a mass analyzer 120, which may be a magnet that allows ionshaving a particular mass to charge ratio to pass through. This massanalyzer 120 is used to separate only the desired ions. It is thedesired ions that then enter the linear accelerator 200.

The linear accelerator 200 comprises one or more cavities 201. Eachcavity 201 comprises a resonator coil 202 that may be energized byelectromagnetic fields created by an excitation coil 205. The excitationcoil 205 is disposed in the cavity 201 with a respective resonator coil202. The excitation coil 205 is energized by an excitation voltage,which may be a RF signal. The excitation voltage may be supplied by arespective RF generator 204. In other words, the excitation voltageapplied to each excitation coil 205 may be independent of the excitationvoltage supplied to any other excitation coil 205. Each excitationvoltage is preferably modulated at the resonance frequency of itsrespective cavity 201.

When an excitation voltage is applied to the excitation coil 205, avoltage is induced on the resonator coil 202. The result is that theresonator coil 202 in each cavity 201 is driven by a sinusoidal voltage.Each resonator coil 202 may be in electrical communication with arespective accelerator electrode 203. The ions pass through apertures ineach accelerator electrode 203.

The entry of the bunch into a particular accelerator electrode 203 istimed such that the potential of the accelerator electrode 203 isnegative as the bunch approaches, but switches to positive as the bunchpasses through the accelerator electrode 203. In this way, the bunch isaccelerated as it enters the accelerator electrode 203 and is repelledas it exits. This results in an acceleration of the bunch. This processis repeated for each accelerator electrode 203 in the linear accelerator200. Each accelerator electrode 203 increases the acceleration of theions.

After the bunch exits the linear accelerator 200, the bunch may passthrough a scanner 150, which serve to create the final ion beam 155containing the desired species of ions. The scanner 150 causes theincoming ion beam to be fanned in the width direction so as to form ascanned ribbon ion beam.

As described above, the platen 160 may be in communication with a platenorientation motor 170. The platen orientation motor 170 may beconfigured to move the platen 160 in any of a plurality of differentdirections. For example, the platen orientation motor 170 may have thecapability to rotate the platen 160. Additionally, the platenorientation motor 170 is configured to tilt the platen 160. Tilt isdefined as a rotation about an axis 161 that is parallel to the widerdimension of the ion beam and passing through the center of the platen160. This tilt is sometimes referred to as X-tilt. The angle of X-tiltmay be referred to as the tilt angle.

The controller 180 may be in communication with the RF generator 204, soas to control the implant energy. In addition, the controller 180 may bein communication with the platen orientation motor 170, so as to adjustthe tilt angle and twist angle of the platen 160. The controller 180 mayalso be in communication with other components, such as the RFgenerators 204.

Of course, the ion implantation system may include other components,such as quadrupole elements, additional electrodes to accelerate ordecelerate the beam and other elements.

A third embodiment is shown in FIG. 1C. Components that are common withFIG. 1A are given identical reference designators.

The semiconductor processing apparatus includes an ion source 100. Incertain embodiments, the ion source 100 may be an RF ion source. Inanother embodiment, the ion source 100 may be an indirectly heatedcathode (IHC). Other embodiments are also possible. For example, theplasma may be generated in a different manner, such as by a Bernas ionsource, a capacitively coupled plasma (CCP) source, microwave or ECR(electron-cyclotron-resonance) ion source. The manner in which the ionsis generated is not limited by this disclosure.

One chamber wall, referred to as the extraction plate, includes anextraction aperture. The extraction aperture may be an opening throughwhich the ions generated in the ion source chamber are extracted anddirected toward a workpiece 10. The extraction aperture may be anysuitable shape. In certain embodiments, the extraction aperture may beoval or rectangular shaped, having one dimension, referred to as thewidth (x-dimension), which may be much larger than the second dimension,referred to as the height (y-dimension). In certain embodiments, aribbon ion beam is extracted from the ion source 100. In otherembodiments, a spot ion beam is extracted from the ion source 100.

Disposed outside and proximate the extraction aperture of the ion source100 are extraction optics 103. In certain embodiments, the extractionoptics 103 comprises one or more electrodes. Each electrode may be asingle electrically conductive component with an aperture disposedtherein. Alternatively, each electrode may be comprised of twoelectrically conductive components that are spaced apart so as to createthe aperture between the two components. The electrodes may be a metal,such as tungsten, molybdenum or titanium. One or more of the electrodesmay be electrically connected to ground. In certain embodiments, one ormore of the electrodes may be biased using an extraction power supply104. The extraction power supply 104 may be used to bias one or more ofthe electrodes relative to the ion source 100 so as to attract ionsthrough the extraction aperture. The voltage applied by the extractionpower supply 104 to the extraction optics 103 may determine the energyof the extracted ions.

Located downstream from the extraction optics 103 is a mass analyzer120. The mass analyzer 120 uses magnetic fields to guide the path of theextracted ions. The magnetic fields affect the flight path of ionsaccording to their mass and charge. A mass resolving device 121 that hasa resolving aperture 122 is disposed at the output, or distal end, ofthe mass analyzer 120.

By proper selection of the magnetic fields, only those ions that have aselected mass and charge will be directed through the resolving aperture122. Other ions will strike the mass resolving device 121 or a wall ofthe mass analyzer 120 and will not travel any further in the system.

A collimator 185 is disposed downstream from the mass resolving device121. The collimator 185 accepts the ions that pass through the resolvingaperture 122 and creates a ribbon ion beam formed of a plurality ofparallel or nearly parallel beamlets.

Located downstream from the collimator 185 may be anacceleration/deceleration stage 190. The acceleration/deceleration stage190 may be referred to as an energy purity module. The energy puritymodule is a beam-line lens component configured to independently controldeflection, acceleration, deceleration, and focus of the ion beam. Forexample, the energy purity module may be a vertical electrostatic energyfilter (VEEF) or electrostatic filter (EF).

In certain embodiments, quadrupole lenses may be disposed in certainpositions in the semiconductor processing apparatus. For example, aquadrupole lens may be disposed between the ion source 100 and the massanalyzer 120, between the mass analyzer 120 and the mass resolvingdevice 121, and/or between the mass resolving device 121 and thecollimator.

Of course, the ion implantation system may include other components,such as a scanner to create a ribbon beam from a spot ion beam, andadditional electrodes to accelerate or decelerate the beam and otherelements.

Thus, in this embodiment, the extraction optics 103 and/or theacceleration/deceleration stage 190 may be referred to as anaccelerator, as these components are used to accelerate the ions to thedesired implant energy.

The final ion beam 155 exits the acceleration/deceleration stage 190 andimpacts the workpiece 10 disposed on the platen 160. The platen 160 maybe in communication with a platen orientation motor 170. The platenorientation motor 170 may be configured to move the platen 160 in any ofa plurality of different directions. For example, the platen orientationmotor 170 may have the capability to rotate the platen 160.Additionally, the platen orientation motor 170 is configured to tilt theplaten 160. Tilt is defined as a rotation about an axis 161 that isparallel to the wider dimension of the ion beam and passing through thecenter of the platen 160. This tilt is sometimes referred to as X-tilt.The angle of X-tilt may be referred to as the tilt angle.

Additionally, the semiconductor processing apparatus includes acontroller 180. The controller 180 may include a processing unit, suchas a microcontroller, a personal computer, a special purpose controller,or another suitable processing unit. The controller 180 may also includea non-transitory computer readable storage element, such as asemiconductor memory, a magnetic memory, or another suitable memory.This non-transitory storage element may contain instructions and otherdata that allows the controller 180 to perform the functions describedherein.

The controller 180 may be in communication with the extraction powersupply 104 and other components, so as to control the implant energy. Inaddition, the controller 180 may be in communication with the platenorientation motor 170, so as to adjust the tilt angle and twist angle ofthe platen 160.

Thus, FIGS. 1A, 1B and 1C all show a semiconductor processing apparatusthat includes an ion source 100, a mass analyzer 120, an accelerator, aplaten 160, a controller 180 and a platen orientation motor 170.

For each implant, there may be an associated recipe, which includes thevoltage applied to the accelerator, the dose, and the tilt and twistangles to be supplied by the platen orientation motor 170.

In operation, a workpiece 10 is disposed on the platen 160 and isimplanted by the final ion beam 155. The workpiece 10 may be a siliconworkpiece. The controller 180 may set the tilt and twist angles to besupplied by the platen orientation motor 170 prior to the implantation.Additionally, the controller 180 may set the voltage to be applied tothe accelerator and the dose to be implanted.

Any of the semiconductor processing apparatus described above may beused to perform a series of implants so as to form an implanted region,having a desired dopant concentration profile.

In certain embodiments, the desired dopant concentration profile may bea rectangular or box profile, wherein the concentration of implantedatoms remains roughly constant over a predetermined thickness.

In this disclosure, thickness is defined as the maximum depth having apredetermined minimum concentration of atoms, less the minimum depthhaving that predetermined minimum concentration of atoms, whereinthroughout the thickness, the dopant concentration is always at leastequal to the predetermined minimum concentration.

As noted above, these implants are typically performed by modifying theimplant energy for each implant so as to deposit ions at a plurality ofdifferent depths. The result is a thick implanted region having aroughly constant dopant concentration profile throughout the desiredthickness. In this disclosure, a thick implanted region may refer to anyimplanted region having a thickness of 1 or more μm. In certainembodiments, a thick implanted region may refer to any implanted regionhaving a thickness of 2 or more μm.

However, to improve the throughput of these operations, each of thesesemiconductor processing apparatuses may be configured such that thesethick implanted regions are formed using a single implant energy.

For example, in one embodiment, it may be desirable to implant hydrogenions into a silicon workpiece to create an implanted region having aminimum concentration of hydrogen atoms that is about 1E18 atoms/cm³.Further, the desired thickness of this implanted region may be about 4.5μm. Additionally, the desired depth of this implanted region may bebetween 3.5 μm and 8.1 μm. In other words, the maximum depth having theminimum concentration is 8.1 μm and the minimum depth having thatminimum concentration is 3.5 μm. In certain embodiments, this implantedregion may be a field stop layer.

FIG. 2 shows four implant profiles as-implanted, where each implant isperformed using the same implant energy. In this test, that implantenergy is 600 keV, however, other implant energies may also be used. Thedose for each implant was set to 2E14 atoms/cm². FIG. 2 and theassociated data reflect the concentration of hydrogen atomsas-implanted, prior to any thermal treatment.

A first implant 300 is performed using a 7° tilt angle and a 0° twistangle. As shown in FIG. 2, most of the hydrogen ions from the firstimplant 300 are implanted at a depth of between 7.0 μm and 8.5 μm. Themaximum concentration is about 4E18 atoms/cm³ and the depth of themaximum concentration (Rp) is at about 7.7 μm. This implant is used toimplant the ions at the greatest depth. Note that the lowest depthwherein the concentration is greater than 1E18 is about 8.1 μm.Therefore, in certain embodiments, the implant energy is selected so asto implant ions to the maximum depth while the tilt angle is at or near0°. In this disclosure, the phrase “at or near 0°” refers to a tiltangle less than 10°. In certain embodiments, the phrase refers to a tiltangle less than 5°. In certain embodiments, the phrase refers to a tiltangle less than 2°.

A second implant 310 is performed using a 30° tilt angle and a 0° twistangle. Most of the hydrogen ions from the second implant 310 areimplanted at a depth of between 5.7 μm and 7.5 μm. The maximumconcentration is about 3E18 atoms/cm³ and the depth of the maximumconcentration (Rp) is at about 6.8 μm.

A third implant 320 is performed using a 45° tilt angle and a 0° twistangle. Most of the hydrogen ions from the third implant 320 areimplanted at a depth of between 4.5 μm and 6.5 μm. The maximumconcentration is about 2.5E18 atoms/cm³ and the depth of the maximumconcentration (Rp) is at about 5.6 μm.

A fourth implant 330 is performed using a 60° tilt angle and a 0° twistangle. Most of the hydrogen ions from the fourth implant 330 areimplanted at a depth of between 3.0 μm and 5.0 μm. The maximumconcentration is about 2E18 atoms/cm³ and the depth of the maximumconcentration (Rp) is at about 4.0 μm.

FIG. 3 shows the hydrogen concentration profile, as-implanted, as afunction of depth after the four implants described in FIG. 2 areperformed. FIG. 3 and the associated data reflect the concentrationsas-implanted, prior to any thermal treatment. Note that theconcentration of hydrogen ions is at least 1E18 from about 3.5 μm toabout 8.1 μm. Thus, an implanted region having a thickness greater than4 μm was formed using four implants having the same implant energy.Furthermore, the concentration is roughly constant, where the ratio ofthe maximum concentration to the minimum concentration throughout thedesired thickness is less than 5.

Further, the concentration profile of FIG. 3 may be further improved.For example, if the dose of the fourth implant 330 is increased, theminimum concentration (which occurs at about 4.8 μm) may be increased.Further, if the dose of the first implant 300 is decreased, the maximumconcentration (which occurs at a depth of about 7.7 μm) may be reduced,while still maintaining the desired minimum concentration throughout thedesired range of depths.

Additionally, additional implants may be performed to fill in thetroughs. For example, one or more implants may be performed at angles ofabout 18°, 37° and/or 57° to further flatten the concentration profile.

Thus, by varying the tilt angle and optionally the dose, it is possibleto create a rectangular concentration profile where the ratio of themaximum concentration to the minimum concentration over the entire rangeof depths is less than 5. In certain embodiments, the ratio is less than4. In some embodiments, the ratio is less than 3. In some embodiments,the ratio is less than 2.

If only the first two implants were performed, an implanted regionhaving a thickness of about 1.8 μm (from about 6.8 μm to about 8.1 μm)would be formed. Further, the ratio of the maximum concentration to theminimum concentration over this range of depths is about 4. However, byadjusting the dose and optionally the tilt angle of these implants, asdescribed above, the ratio may be reduced to less than 3 or less than 2,in some embodiments.

If only the first three implants were performed, an implanted regionhaving a thickness of about 3.1 μm (from about 5.0 μm to about 8.1 μm)would be formed. Further, the ratio of the maximum concentration to theminimum concentration over this range of depths is about 4. However, byadjusting the dose and optionally the tilt angle of these implants, asdescribed above, the ratio may be reduced to less than 3 or less than 2,in some embodiments.

Note that the straggle associated with each implant increases withincreased tilt angle. In other words, the width of the dopantconcentration profile for a particular implant typically becomes largeras the tilt angle of that implant increases. Thus, the distance betweenthe Rp of the higher tilt angle implants may be greater than thedistance between the Rp of the lower tilt angle implants. Morespecifically, the distance between the Rp of the fourth implant 330 andthe third implant 320 is about 1.6 μm. In contrast, the distance betweenthe Rp of the second implant 310 and the first implant 300 is only about0.9 μm. However, because of the increased straggle at higher tiltangles, the combination of these implants results in a broader profilewhere the concentration is at or above about 1E18.

Thus, in certain embodiments, the tilt angles are selected based on theminimum desired concentration and the straggle associated with eachimplant. In this embodiment, each implant creates a concentrationprofile that resembles a bell curve. The width of the bell curveincreases with increasing tilt angle, while the height of the bell curvedecreases with increasing tilt angle.

In other words, the tilt angles may be selected such that the minimumconcentration between any two adjacent Rp is above a predeterminedminimum. For example, the predetermined minimum for FIG. 3 may be 1E18atoms/cm³. As shown in the figure, the minimum between the Rp of firstimplant 300 and the Rp of second implant 310 is about 1.2E18. Theminimum between the Rp of second implant 310 and the Rp of third implant320 is about 1.1E18. Finally, the minimum between the Rp of thirdimplant 320 and the Rp of fourth implant 330 is about 1.0E18.

In certain embodiments, the first tilt angle is selected to be at ornear 0°. The next tilt angle may be selected such that the lower depthat which that implant provides a concentration equal to about 50% of thepredetermined minimum is the same as the upper depth at which the firstimplant provides a concentration equal to or slightly greater than 50%of the predetermined minimum. For example, as shown in FIG. 2, the firstimplant 300 provides a concentration of about 5E17 atoms/cm³ (which is50% of 1E18) at an upper depth of 7.3 μm. Similarly, the second implant310 provides a concentration of about 5E17 atoms/cm³ at a lower depth of7.3 μm, and an upper depth of 6.2 μm. The second implant 310 may beperformed at a tilt angle greater than the first tilt angle, such asbetween 10° and 40°. The third implant 320 provides a concentration ofabout 5E17 atoms/cm³ at a lower depth of 6.2 μm, and an upper depth of4.8 μm. The third implant 320 may be performed at a tilt angle greaterthan the second tilt angle, such as between 30° and 60°. Lastly, thefourth implant 330 provides a concentration of about 5E17 atoms/cm³ at alower depth of 3.2 μm. The fourth implant 330 may be performed at a tiltangle greater than the third tilt angle, such as between 40° and 70°.

Thus, as shown in FIG. 3, a field stop layer having a hydrogenconcentration of greater than 1E18 ions/cm³ and thickness of about 4.5μm may be created using a single implant energy. Further, the ratio ofthe maximum concentration to the minimum concentration is less than 5.As stated above, by varying the dose of each implant, the ratio may bereduced. Further, by adding additional implants, using the same implantenergy and other tilt angles, the ratio can be reduced. Thus, the ratiomay be less than 4, less than 3 or less than 2.

This technique is also useful for other semiconductor applications.

For example, this technique is not limited to hydrogen ions.

For example, any desired species, including but not limited to boron,arsenic, and phosphorus may be used.

Furthermore, this technique may be used to create other types ofimplanted regions.

In another example, a photodiode may be fabricated with a deep trenchimplanted region. This implanted region may be about 2 μm in thicknessand may have a boron concentration of about 1E16 atoms/cm³. In certainembodiments, this implanted region may typically be created using morethan 6 different implant energies.

In accordance with one embodiment, using the present technique, thisimplanted region may be fabricated using a single implant energy and twoor more different tilt angles.

In another embodiment, this implanted region may be created using two ormore implant energies, where two or more implants at different tiltangles are performed at each implant energy. For example, the implantedregion may be created by performing implants at a first implant energy,with two or three different tilt angles and implants at a second implantenergy, with two or three different tilt angles. In this case, a delayis incurred when changing the implant energy from the first implantenergy to the second implant energy. However, this delay is far lessthan the delays associated with 6 different implant energies.

Further, the present technique may be used to create gradient profiles.A gradient profile is one where the log of the dopant concentrationprofile varies roughly linearly as a function of depth. For example, awell may be N-doped where the maximum concentration occurs at a depth ofabout 0.1 μm and decreases exponentially to a depth of about 1.0 μm. Forexample, the concentration may decrease by a factor of about 35 over 0.9μm. In certain embodiments, the decrease in concentration may appearroughly linear when plotted in log-linear, also referred to as semi-log,format. Using a single implant energy, with several different tiltangles, a similar concentration profile may be created.

This gradient profile may be used to create wells for logic devices. Inthose logic devices, a well is typically created beneath the gate in atransistor. Depending on the type of transistor, the well may be dopedwith a P-type dopant, such as boron, or an N-type dopant, such asphosphorus.

FIG. 4 shows a simulation of a resultant gradient dopant concentrationprofile 400, as-implanted, that was created using one implant energy andthree different tilt angles. In this example, the implant energy was 180keV and the implanted species is phosphorus. Of course, other speciesand implant energies may be used. For example, any desired species,including but not limited to boron, arsenic, and hydrogen may be used.

FIG. 4 and the associated data reflect the concentrations as-implanted,prior to any thermal treatment. In this figure, the dopant concentrationdecreases roughly linearly from about 0.2 μm to about 1.1 μm, whenviewed on a semi-log graph. Specifically, in this gradient profile, theconcentration decreases from 4E18 atoms/cm³ to about 2E16 atoms/cm³ overthis range of depths. If the gradient profile decreased exactly linearlyon the semi-log graph, the equation of the line 401 over the desiredrange of depths may be expressed as:log(y)=mx+b, where y is the concentration,m is the slope; and b is the yintercept.

The graph shown in FIG. 4 shows that the resultant gradient dopantconcentration profile 400, as-implanted, deviates from this straightline 401 by less than a factor of 2 throughout the desired range ofdepths. In this disclosure, the phrase “roughly linearly” means that theactual dopant concentration deviates from a straight line 401 by afactor of 2 or less when plotted on a semi-log graph. In certainembodiments, the deviation may be less than a factor of 1.5. In otherembodiments, the deviation may be less than a factor of 1.25.

FIG. 5 shows the simulation of the three implants, as-implanted, thatwere used to create the dopant profile shown in FIG. 4. Again, FIG. 5and the associated data reflect the concentrations as-implanted, priorto any thermal treatment. Note that the first implant 500 does not showthe bell shape that was evident in FIG. 2. This is because the tiltangle of this first implant 500 was selected to allow channeling ofatoms in the workpiece. This channeling effect produces a more constantdopant profile of about 1E17 atoms/cm3 across the range of depths fromabout 0.2 μm to about 0.95 μm. In one embodiment, this first implant 500may be performed at a dose of 1E13, a tilt angle of 0° and a twist angleof 0°. The second implant 510 occurs at an angle greater than that ofthe first implant 500 and shows a peak concentration at about 0.3 μm andthe maximum concentration of about 2E18. The dose of the second implant510 may be greater than that of the first implant 500, such as but notlimited to 5E13. The first implant 500 and second implant 510 providethe desired gradient profile for depths greater than about 0.4 μm. Thethird implant 520 is used to provide the greater concentration that isfound at depths less than 0.4 μm. The dose of the third implant 520 maybe the same as the dose of the second implant 510. Thus, to implant atthese shallow depths, the tilt angle of the third implant 520 may beincreased, such as to a value of 30° or greater. The doses of thesethree implants may be the same or may be different. For example, asdescribed above, the first implant 500 may be performed at a lower doseto provide the constant dopant profile shown in the figure. In certainembodiments, the first implant 500 may not be performed, as the secondimplant 510 and third implant 520 may also produce a gradient profile.

Further, as described above, the shape of the concentration profile maybe further improved by varying the dose of each implant. Additionally,additional implants at tilt angles between the minimum and maximum anglemay be used to further improve the shape of the concentration profile.The implant energy was determined based on the maximum depth of thedesired concentration profile. Like the box profile, the first implantmay be performed at an angle that is at or near 0°. The second tiltangle may be greater than the first tilt angle, such as between 1° and30°. The third tilt angle may be greater than the second tilt angle,such as between 30° and 65°.

The values noted above are intended to create a profile having agradient similar to that shown in FIG. 4. If a more steep or moregradual gradient is desired, the tilt angles and doses may be adjustedaccordingly. Similarly, if the desired concentrations are different thanthose shown in FIG. 4, the tilt angles and doses may be adjusted.

Thus, in addition to rectangular or box profiles, the present techniquealso allows the creation of gradient concentration profiles, using asingle implant energy with multiple tilt angles.

This disclosure is not limited to the creation of box and gradientprofiles. Rather, the use of a single implant energy and multiple tiltangles may also be used to create other shaped dopant concentrationprofiles.

The system and method described herein have many advantages. In onetest, it was determined that field stop layer having a thickness of 4.5μm can be formed using a single implant energy of 600 keV. This fieldstop layer was performed using four different tilt angles. In contrast,this field stop layer is traditionally fabricated using three or moredifferent implant energies. It was noted that the time to change theimplant energy and then recalibrate all of the components of thesemiconductor processing apparatus to each new implant energy can be aslong as 5 to 6 minutes. Thus, the ability to achieve implanted regionshaving a thickness in excess of 1 μm without changing the implant energymay substantially reduce the time to form the implanted region.

Similarly, typically a graded P-well or N-well is fabricated using threeor more different implant energies. The ability to fabricate thesestructures with a single implant energy may substantially increasethroughput. For example, a gradient profile, similar to that createdusing three different implant energies, was created using a singleimplant energy and three different tilt angles. This results in asignificant improvement in throughput and efficiency.

Likewise, an isolation trench for a photodiode may have a thickness ofabout 2 μm and a concentration of 2E16 boron atoms/cm³. In certain priorart applications, this isolation trench is fabricated using 6 or moredifferent implant energies. By using a single implant energy and avariety of tilt angles, the time to fabricate this isolation trench canbe reduced significantly. In fact, even if two different implantenergies are used to create this isolation trench, the throughput isstill much improved as compared to the current process.

Thus, the present system and method reduces the time to create animplanted region with the desired dopant concentration profile. As notedabove, when the implant energy is varied, the voltages applied tovarious electrodes, accelerators, acceleration/deceleration stages,magnets, and focusing elements are changed. Modifying these voltages maytake many minutes. However, only the platen orientation motor 170 isadjusted to change the tilt angle, which needs no additional tuningafter being moved.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. A method of forming an implanted region having arectangular concentration profile within a semiconductor workpiece,comprising: performing a first implant on the semiconductor workpiece,wherein the first implant is performed at a predetermined implant energyand a first tilt angle, wherein a maximum concentration of ionsimplanted by the first implant occurs at a first depth; and performing asecond implant on the semiconductor workpiece, wherein the secondimplant is performed at the predetermined implant energy and a secondtilt angle, wherein a maximum concentration of ions implanted by thesecond implant occurs at a second depth, less than the first depth;wherein the second tilt angle is selected such that, after the first andsecond implants are performed, a minimum concentration between the firstdepth and the second depth is greater than a predetermined minimumconcentration.
 2. The method of claim 1, wherein the first tilt angle isat or near 0° and the predetermined implant energy is selected such thefirst depth is at a desired depth.
 3. The method of claim 1, furthercomprising: performing a third implant on the semiconductor workpiece,wherein the third implant is performed at the predetermined implantenergy and a third tilt angle, greater than the second tilt angle,wherein a maximum concentration of ions implanted by the third implantoccurs at a third depth, less than the first depth and the second depth;wherein the third tilt angle is selected such that, after the first,second and third implants are performed, a minimum concentration betweenthe first depth and the third depth is greater than the predeterminedminimum concentration.
 4. The method of claim 3, wherein a thickness ofthe implanted region, wherein thickness is defined as a maximum depthhaving a concentration greater than the predetermined minimumconcentration, less a minimum depth having the concentration greaterthan the predetermined minimum concentration, is greater than 1 μm. 5.The method of claim 4, wherein the thickness of the implanted region isgreater than 2 μm.
 6. The method of claim 3, wherein a ratio of amaximum concentration between the first depth and the third depth to theminimum concentration is less than
 5. 7. The method of claim 6, whereinthe ratio of the maximum concentration to the minimum concentration isless than
 4. 8. The method of claim 7, wherein the ratio of the maximumconcentration to the minimum concentration is less than
 3. 9. The methodof claim 3, wherein the first implant is performed with a first dose,the second implant is performed with a second dose and the third implantis performed with a third dose, wherein the first dose, the second doseand the third dose are not all the same value.
 10. The method of claim3, wherein one or more additional implants are performed at additionaltilt angles, between the first tilt angle and the third tilt angle, soas to reduce a ratio of a maximum concentration between the first depthand the third depth to the minimum concentration.
 11. A method offorming an implanted region having a gradient concentration profilewithin a semiconductor workpiece, comprising: performing a first implanton the semiconductor workpiece, wherein the first implant is performedat a predetermined implant energy, a first dose and a first tilt angle;and performing a second implant on the semiconductor workpiece, whereinthe second implant is performed at the predetermined implant energy, asecond dose and a second tilt angle; wherein the first tilt angle, thefirst dose, the second tilt angle, and the second dose are selected suchthat, after the first and second implants are performed, a concentrationof implanted atoms decreases between a first depth and a second depth.12. The method of claim 11, wherein, when plotted on a semi-log graph, aprofile of the concentration of implanted atoms decreases roughlylinearly between the first depth and the second depth.
 13. The method ofclaim 11, wherein the first dose is different from the second dose. 14.The method of claim 11, further comprising: performing a third implanton the semiconductor workpiece, wherein the third implant is performedat the predetermined implant energy, a third dose and a third tiltangle; wherein the third tilt angle and the third dose are selected suchthat, after the first, second and third implants are performed, whenplotted on a semi-log graph, a profile of the concentration of implantedatoms decreases roughly linearly between the first depth and the seconddepth.
 15. The method of claim 14, wherein one of the implants isperformed at a tilt angle to allow channeling of atoms in thesemiconductor workpiece.